This invention relates to an electrical contact element having a core part made of an iron/nickel alloy with a gold/tin alloy applied to a portion of the core part serving as a solderable connection therefor.
Contact elements of this type are soldered, by means of the gold/tin alloy, onto a support, for example a ceramic substrate, and serve to establish electrical contacts with further electrotechnical or electronic components. The gold/tin alloy serving as the solderable connection should, in this case, cover only that portion of the core part which is to be soldered directly to the support. As the core part conventionally comprises base metals or alloys thereof, the problem is that of finding a suitable adhesive layer which, when used between the core part and the gold/tin alloy, not only ensures the necessary electrical properties such as conductivity, contact resistance etc., but also ensures that the gold/tin alloy remains on the portion of the core part intended therefor and does not accidentally wet further regions of the surface of the core part.
The material used for such an adhesive layer is usually gold. Such a gold layer has the required properties and at the same time avoids the wetting of an unintentionally large portion of the surface of the core part with the gold/tin alloy, so that the size of the wetted area can be accurately controlled by means of the quantity of the gold/tin alloy applied to the core part. However, in those contact elements in which the solderable area, that is the area to be wetted with the gold/tin alloy, is relatively large in proportion to the total surface of the contact element, the use of an adhesive layer made of gold significantly increases the costs of the contact element.
It is therefore an object of the present invention to find a material for the adhesive layer which, while ensuring approximately identical electrical and physical/chemical properties, is cheaper than gold and at the same time, like gold, prevents the uncontrolled running of the gold/tin alloy on the surface of the contact element.